1. Field of the Invention
This invention relates to emulsion type adhesive compositions which includes a copolymer of a hydrocarbon diene and an ethoxylated alkyl amine salt of styrene sulfonate which is prepared by an emulsion polymerization process, wherein the sulfonated copolymer is reacted with a metallic base to form an ethoxylated alkylamine and a metal neutralized sulfonated copolymer which has about 5 to about 125 meq. of metal neutralized sulfonate groups per 100 grams of the metal neutralized sulfonated copolymer and less than about 300 parts by weight of a hydrocarbon resin of a petroleum or coal tar distillate, formed from dienes and monolefins generally about five and six carbon atoms per 100 parts by weight of the neutralized sulfonated copolymer.
Broadly speaking, synthetic adhesives used in packaging can be classified into four categories: water based emulsion system, solvent based, reactive and hot melt adhesives. Of these four, currently the water based are used most extensively. Usually the water based adhesives are based on emulsion polymers and are applied to porous cellulosic substrates. Energy from the outside in some fashion is applied to the system to evaporate the water in order that a strong bond may be formed.
With the solvent-based adhesives usually a good wetting is achieved; however, their use has been becoming extremely restrictive due to expensive energy requirements for the evaporation of organic solvents, fire hazards associated with the use of these organic solvents and emissions problems with said solvents. The strict government environmental regulations and restrictions concerning worker's exposure to solvent vapors, etc. has placed extra pressure on the packager to use non-solvent based adhesives.
The hot melt adhesives are generally applied (as the name implies) by conventional extrusion or coating techniques in the temperature range of 250.degree. to 450.degree. C. on one of the surfaces to be bonded. The other surface is brought in contact with the hot surface for a sufficient period of time for the melt to cool, where upon solidification, a strong and durable bond is formed.
As a result of various local and federal safety and environmental regulations, the polymers adhesive industry is moving from solvent to water-based technology. Usually the water based pressure sensitive adhesives are based on emulsion polymers and applied to porous cellulosic substrates. Energy is applied to the system to evaporate the water in order to form a strong bond. The key requirement of such an emulsion is that it form a uniform coating having good adhesive (tack) and cohesive characteristics. The degree of the adhesive and cohesive strength of the final adhesive product is established by its end use. For example, for general label applications, it is desired that the product have aggressive tack and not so much cohesive strength. However, for general tape uses, the composition should have good cohesive strength with marginal tack properties.
Currently in the market, there are very limited emulsion polymers available for water based adhesives. A few acrylic polymer emulsions are available which are suitable for label applications but these are relatively expensive. There is not a single water based polymeric adhesive available in the market which meets the requirements for tape applications, especially the tapes desired by the automotive painting industry.
2. Prior Art
Several U.S. patents have described sulfonated polymers such as sulfonated butyl polymers and sulfonated EPDM polymers in adhesive applications (e.g., U.S. Pat. No. 3,867,247 and U.S. Pat. No. 3,801,531). It is important to distinguish the instant invention over those prior art systems. The former patents are directed at a sulfonated butyl cement or EPDM terpolymer which is solvent based and is employed to laminate various substrates. It is important to note that the instant invention differs dramatically from these patents as follows:
(a) The adhesives of the instant invention are not deposited from solvents, but are water based emulsions;
(b) The instant invention may optionally include either a tackifier resin and/or plasticizer capable of associating with the neutralized sulfonate groups.
(c) The instant invention is directed to metal neutralized sulfonated elastomeric copolymers, whereas most of the prior art deals with sulfonated butyl rubber (e.g., U.S. Pat. No. 3,867,247).